Solar Energy Perspectives - IEA

Solar Energy Perspectives: Solar photovoltaics
Figure 6.1 The photovoltaic effect
Junction
Current
Load
Photons
Electron flow
N-type silicon
P-type silicon
“Hole” flow
Source: EPIA, 2011.
Key point
Photovoltaic systems directly convert light into electricity.
PV cells, modules and systems have an excellent track record of progressive cost reductions,
with a learning rate of about 20% for modules, and about 12.5% for systems. This means that
each doubling of the cumulative installed capacity has led to a cost reduction for modules of
about 20%. 1 The historical learning rate for PV modules was actually 22.8% per year on
average over 1976-2003.
Three major factors driving cost reductions from 1980 to 2001 have been identified: manufacturing
plant size, module efficiency and purified silicon cost. The driving role of scaling-up in cost
reduction is also demonstrated by the success of some new entrants, which were able to raise
capital and take on the risk of large investments but offered no technical superiority. Ten out of
the 16 major advances in module efficiency can be traced back to government and university
research and development programmes, while the other six were accomplished in companies
manufacturing PV cells. Finally, reductions in the cost of purified silicon were a spill-over benefit
from manufacturing improvements in the microprocessor industry (Nemet, 2006).
From 2004 to 2007, however, a bottleneck in the production of purified silicon led to a steep
increase in its cost (Figure 6.2), resulting in a slight increase in PV costs, seemingly a violation
of the learning curve concept.
1. Progress ratio is another way of expressing the same reality and is calculated at 1 minus the learning rate, or about 80% in this
case (the lower the progress ratio, the faster the progress).
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© OECD/IEA, 2011